1. Types of Sensory Neurons
PHYSICAL:
Photoreceptors (for vision)
Mechanoreceptors (for touch & hearing)
CHEMICAL:
Also known as “Chemoreceptors”:
Odor receptors
(for smell)
Gustatory receptors (for taste)

3. Taste buds contain sensory neurons w/ taste receptors

4. Hearing

5. Exploring the structure of the human ear
Pinna
Auditory canal
Eustachian tube
Tympanic membrane
Stapes
Incus
Malleus
Skull bones
Semicircular canals
Auditory nerve, to brain
Cochlea
Oval window
Round window
Vestibular canal
Tympanic canal
Auditory nerve
Bone
Cochlear duct
Hair cells
Tectorial membrane
Basilar membrane
To auditory nerve
Axons of sensory neurons 1
Overview of ear structure 2
The middle ear and inner ear 4
The organ of Corti 3
The cochlea
Organ of Corti
Outer ear
Middle ear
Inner ear
Figure 49.8

6. Hair cells containing mechanoreceptors are inside the cochlea

7. Axons of sensory neurons
Cochlea
Stapes
Oval window
Apex
Axons of sensory neurons
Round window
Basilar membrane
Tympanic canal
Base
Vestibular canal
Perilymph
Cochlea (uncoiled)
Basilar membrane
Apex (wide and flexible)
Base (narrow and stiff)
500 Hz (low pitch)
1 kHz
2 kHz
4 kHz
8 kHz
16 kHz (high pitch)
Frequency producing maximum vibration

8. The Vertebrate Eye

9. The structure of the vertebrate eye
Ciliary body
Iris
Suspensory ligament
Cornea
Pupil
Aqueous humor
Lens
Vitreous humor
Optic disk (blind spot)
Central artery and
vein of the retina
Optic nerve
Fovea (center of visual field)
Retina
Choroid
Sclera
Figure 49.18

10. Humans and other mammals
Focus light by changing the shape of the lens
Lens (flatter)
Lens (rounder)
Ciliary muscle
Suspensory ligaments
Choroid
Retina
Front view of lens and ciliary muscle
Ciliary muscles contract, pulling border of choroid toward lens
Suspensory ligaments relax
Lens becomes thicker and rounder, focusing on near objects
(a) Near vision (accommodation)
(b) Distance vision
Ciliary muscles relax, and border of choroid moves away from lens
Suspensory ligaments pull against lens
Lens becomes flatter, focusing on distant objects
Figure 49.19a–b

11. Lateral view of the vertebrate eye

12. 2 Types of Photoreceptors:
RODS:
More numerous (125 x 106)
More sensitive to light
Responsible for night vision
Absent from the fovea
Lower resolution
CONES:
Less numerous
Sensitive to (wavelength)
Responsible for color vision
Come in 3 types: red, green, blue (photopsins)
Higher resolution

13. Photoreceptors in the retina

14. Looking inside a photoreceptor

15. Retinal pigment changes shape when light strikes it

16. Signal Transduction in Rods
EXTRACELLULAR FLUID
Membrane potential (mV)
– 40
– 70
Dark Light
– Hyper- polarization
Time
Na+
cGMP
CYTOSOL
GMP
Plasma membrane
INSIDE OF DISK
PDE
Active rhodopsin
Light
Inactive rhodopsin
Transducin
Disk membrane
2 Active rhodopsin in turn activates a G protein called transducin.
3 Transducin activates the enzyme phos-phodiesterae(PDE).
4 Activated PDE detaches cyclic guanosine monophosphate (cGMP) from Na+ channels in the plasma membrane by hydrolyzing cGMP to GMP.
5 The Na+ channels close when cGMP detaches. The membrane’s permeability to Na+ decreases, and the rod hyperpolarizes.
1 Light isomerizes retinal, which activates rhodopsin.
Absorption of light by retinal
Triggers a signal transduction pathway
Figure 49.21

17. Three other types of neurons contribute to information processing in the retina
Ganglion cells, horizontal cells, and amacrine cells
Optic nerve fibers
Ganglion cell
Bipolar cell
Horizontal cell
Amacrine cell
Pigmented epithelium
Neurons
Cone
Rod
Photoreceptors
Retina
Optic nerve
To brain
Figure 49.23

19. A bird’s eye view…

20. An overview of visual processing

21. Message travels from RETINA to VISUAL CORTEX (oc.lobe)

22. The brain tries to make sense of missing visual information
You see a white triangle even though no triangle exists.

24. Which yellow line is longer?
The brain applies perspective to understand different sizes